The basic hydrometallurgical process for recovering metallic copper from copper sulfide ore concentrates, such as chalcopyrite is described in U.S. Pat. Nos. 3,785,944 and 3,879,272, both commonly assigned, and incorporated by reference herein in their entirety.
The process as disclosed in U.S. Pat. No. 3,785,944 has four distinct stages: (a) A reduction stage in which fresh copper sulfide ore concentrate, especially chalcopyrite, is reacted with an aqueous chloride solution containing cupric chloride, ferrous chloride, and a small amount of ferric chloride to form a solution that contains cuprous chloride and ferrous chloride; (b) A metal recovery stage where the reduced solution from the reduction stage is electrolyzed to produce metallic copper at a cathode and with cupric chloride regenerated at an anode; (c) A regeneration-purge stage where the ferrous chloride and remaining cuprous chloride in the spent electrolyte from the metal recovery stage are oxidized with air or oxygen to produce an aqueous chloride solution that contains cupric chloride and ferric chloride while concurrently precipitating excess iron as basic iron oxides and sulfate ions as jarosite; and, (d) An oxidation stage where the partially reacted copper sulfide ore concentrate from the reduction stage is further oxidized by the solution from the regeneration-purge stage to complete the solubilization of the copper therefrom while producing a solution that consists of cupric chloride, ferrous chloride, and a small amount of ferric chloride which is then recycled to the reduction stage after removal of the precipitated solids.
U.S. Pat. No. 3,879,272, a continuation-in-part of U.S. Pat. No. 3,785,944, enhanced the basic process by teaching: (a) The advantage of a three stage process obtained by combining into one stage the regeneration-purge stage and the oxidation stage; (b) The improved performance of the reduction stage by use of increased chloride ion concentrations obtained by using mixtures of sodium chloride, potassium chloride, and/or magnesium chloride; and, (c) The advantage of using potassium chloride to precipitate potassium jarosite, thereby effecting an essentially complete purge of sulfate ions from the solution during the operation of the combined regeneration-purge-oxidation stage.
The process, as outlined above, is effective in the commercial production of metallic copper from copper sulfide ore concentrates. However, the process does not allow for the economic recovery of other commercially valuable components of the concentrate or the residue waste, such as: elemental sulfur, compounds of molybdenum, or, if present, gold.
Inherent in the operation of the electrolytic step of the metal recovery stage is another disadvantage. U.S. Pat. No. 3,785,944 restricts the amount of " . . . metallic copper produced at the cathode to be not more than about one-half of the cuprous copper in the cuprous chloride solution feed to the electrolytic cells . . . ". During the continuous operation of the process, it frequently happens that much more than one-half of the copper in the electrolytic cell feed solution must be removed in order to assure an overall process metallurgical balance. When this occurs, there no longer exists a balance between the cuprous chloride that is reduced to metallic copper at the cathode and cuprous chloride that is oxidized to cupric chloride at the anode. This imbalanced condition will also arise if the electrolytic cell feed solution contains some unreduced cupric chloride. In this situation, the cathodic reduction of cupric chloride to cuprous chloride causes the equivalent anodic oxidation of cuprous chloride to cupric chloride thereby depleting The inventory of cuprous chloride in the anolyte that balances the cathodic reduction of cuprous chloride to metallic copper. These imbalances are a problem because cuprous chloride undergoes anodic oxidation more rapidly and more easily than do ferrous chloride or chloride ion. As a result, once the anodic reserves of cuprous chloride are depleted, some chlorine gas is liberated at the anode despite the presence of ferrous chloride in the solution surrounding the anode. This condition of chlorine gas evolution causes more rapid degradation of the anode and may create a health hazard for those involved with the operation of the electrolytic cells. These problems are aggravated when the tank house is operated at very high current densities (i.e., anodic current densities that are greater than about 500 amperes per square meter).
One other disadvantage of the described process is the susceptability of the final stage of leaching, the oxidation stage or the combined regeneration-purge-oxidation stage, to process upsets that results in either poor dissolution of the copper sulfide minerals, or excessive precipitation of iron with subsequent precipitation of copper oxychlorides that are lost with the residue waste.
At the present time, there are no known hydrometallurgical processes that have been designed to recover metallic copper from copper sulfide ore concentrates that also: (a) permits the potential economic recovery of elemental sulfur, compounds of molybdenum, and other valuable components of the concentrate or residue waste; (b) prevents anode damage and hazardous chlorine gas evolution caused by metallurgical upsets; and (c) ensures constant maximal solubilization of the copper sulfide minerals despite process upsets. The process of this invention is designed to meet these needs.